Polysuccinimides, polyaspartates, as well as co-polymers thereof are becoming increasingly useful as mineral scale inhibitors, plant nutrient absorption enhancers, additives for cosmetics and personal care products, adhesives, anti-redeposition agents for detergents, dispersants, additives for paper-making, corrosion inhibitors, metal working fluids, lubricants for conveyor belts, additives for the prevention of encrustation in sugar manufacture, and tartar preventative agents in toothpaste.
Methods are known for the production of polysuccinimide by the polymerization of aspartic acid in the presence of various catalysts, such as phosphoric acid in addition to oxygen-containing and sulfur-containing dehydrating agents. However, these prior art methods rely on a relatively inefficient process of heat transfer during polymerization, namely the heating of a semi-solid, viscous mixture which is difficult to stir and therefore cannot be heated uniformly. Other disadvantages are the relatively large amount of catalyst and/or dehydrating agent which is required for polymerization to occur and the subsequent removal of excess catalyst. Attempts to perform catalytic polymerizations in a liquid medium have been made (U.S. Pat. No. 5,484,945 to Nagatomo et. al.), but exceedingly high amounts of catalyst were required to achieve the polymerization of the desired high molecular weight products. The synthesis of polysuccinimide by the polycondensation of aspartic acid in various solvents including thioethers, also has been recently described (Nakato et. al. Polymer Preprints, vol 37, no. 1034, pg 555-556 March 1996!).